Tuesday’s East Sands Leisure Centre incident is the third time this year a UK swimming pool chemical leak has caused a major emergency services response.
Forty people were taken to hospital at the Wild Duck Holiday Park at Belton, near Great Yarmouth, in June after grit jammed a control switch.
Seven casualties were kept in hosptal overnight in the incident and swimmers were treated for breathing and asthma problems.
In July 25 firefighters were called to the Sandy Balls Holiday Park in the New Forest after chlorine leaked from a pump linked to the swimming pool there.
One man was overcome by fumes but was treated at the scene by paramedics.
A 200-metre cordon had to be set up around the site in Fordingbridge as crews from four fire stations used granules to absorb the chemical.
And 10 people were taken to hospital following a suspected chlorine leak at a Leicestershire gym in November 2012.
The David Lloyd Leisure club in Narborough was evacuated after a strong smell of gas was noticed in the pool area.
Goresbrook Leisure Centre in Dagenham was closed for almost two days after a chlorine spillage was found in the plant room of the pool in May 2011.
Three staff members suffered breathing difficulties as a result of the incident but no one was hospitalised.
Almost 50 people, the majority of them children, had to be treated after a chlorine leak at Coseley Swimming Pool in the West Midlands in April 2009, after youngsters complained of watery eyes and difficulty breathing.